Heretofore composite structures of laminated reinforced plastic have been attached to a surface of a supporting structure by forming a flange at the edge of the composite structure and clamping the flange to the supporting structure. Holes were drilled in the flange and supporting structure and bolts inserted in the holes for bolting the flange to the supporting structure. Where the walls of the composite structure must be substantially thick to provide the necessary strength, it has not been feasible to provide a flange at the edge of the composite structure. Also, where the walls of the composite structure are of a thickness where flanges can be formed at the edge, there may be problems with shear failure and delamination due to the concentration forces at the flanges.